Toner for developing electrostatic latent image, charge control agent for use in the toner, and process for preparing the charge control agent

ABSTRACT

A toner for developing an electrostatic latent image is disclosed, which contains as a charge control agent a trivalent chromium salt of salicylic acid or a derivative thereof represented by the following general formula;  
                 
 
     wherein  
     R 1 , R 2  and R 3  each represents a hydrogen atom, a saturated or unsaturated, straight or branched alkyl group or, when taken together, R 1  and R 2  or R 2  and R 3  form a fused ring optionally having a saturated or unsaturated, straight or branched alkyl group, and n represents  0, 1  or  2 . The trivalent chromium salts are formed by adding an aqueous solution of alkali metal salt of salicylic acid or a derivative thereof having a pH of  6.5  to less than  7.0  to an aqueous solution of a chromium(III) halide having a pH of  3.0  to  5.8.

BACKGROUND OF THE INVENTION

[0001] (a) Technical Field of Invention

[0002] This invention relates to a toner for developing an electrostaticlatent image formed by electrophotography, electrostatic recordingprocess, or the like, to a charge control agent for use in producing thetoner, and to a process for preparing the charge control agent.

[0003] (b) Background of the Art

[0004] As a process for developing an electrostatic latent image formedon an electrostatic image carrier such as an electrophotographic lightsensitive member or an electrostatic recording medium, there have beenknown a wet type developing process of using a liquid developercontaining a fine toner dispersed in an electrically insulating liquidand a dry type developing process of using a toner containing acolorant, a magnetic particle, etc. dispersed in a binder resin. The drytype developing process includes a process of using a two-component typedeveloper composed of a carrier and a toner, and a process of using aone-component type developer composed of a toner alone (usually amagnetic toner).

[0005] These toners for developing an electrostatic latent image containa colorant such as a dye or a pigment with binder resin and, withmagnetic toners, further magnetic particles etc. Usually, however, thesecomponents fail to impart desirable charging properties. Therefore, acharge control agent has been used in the toners. As typical examples ofconventionally used charge control agents capable of imparting positivecharge to toner particles, there are illustrated electron donativematerials such as basic dyes (e.g., Nigrosine dyes, triarylmethane dyes,etc.) and quaternary ammonium salts and, as typical examples of thosecapable of imparting negative charge to toner particles, there areillustrated metal-containing dyes such as metal complexes of monoazodyes, chromium-containing organic dyes (e.g., Copper PhthalocyanineGreen, chromium-containing monoazo dyes, etc.). However, many of theseconventional charge control agents have such problem as that they failto impart good charge control properties to toner particles over a longperiod of time due to their insufficient dispersibility in tonerparticles owing to their poor compatibility or wetting properties with abinder resin, or due to their poor stability or some sublimationproperties. Further, some conventional charge control agents are coloredand are not suited for color toners.

[0006] (c) The Prior Art

[0007] As charge control agents capable of solving these problems, therehave been proposed metal complexes of salicylic acid and derivativesthereof (e.g., Japanese Examined Patent Publication No. S55-42752,Japanese Unexamined Patent Publication Nos. H7-84412 and H9-34177, etc.)and divalent metal salts of salicylic acid and derivatives thereof(e.g., Japanese Examined Patent Publication No. H7-62766, etc.). Many ofthese charge control agents are only slightly colored and can beadvantageously used in color toners. However, further study is requiredas to uniform dispersibility in resin and charge control properties.

[0008] As has been described above, charge control agents to be used intoner particles for developing an electrostatic latent image arerequired to have good compatibility or wettability with toner binderresins, good stability, and no colors as well as charge control ability.In addition, they are required to provide toner particles having goodstorage stability, enough durability to be repeatedly used many timesand not to exert adverse influences on fixing property or anti-offsetproperty.

SUMMARY OF THE INVENTION

[0009] It is, therefore, an object of the invention to provide a tonerfor developing an electrostatic latent image, which can solve theabove-described problems and show excellent properties, a charge controlagent having excellent properties, and a process for preparing thecharge control agent.

[0010] Other objects, features and advantages of the present inventionwill become apparent from the detailed description of the preferredembodiments of the invention to follow.

[0011] As a result of intensive investigations, the inventors have foundthat trivalent chromium salts of salicylic acid or its derivativeproduced under specific conditions can satisfy the above-describedrequirements, thus having completed the present invention based on thefinding.

[0012] That is, according to the present invention, there is provided aprocess for preparing a trivalent chromium salt of salicylic acid or itsderivative, which comprises adding an aqueous solution of an alkalimetal salt of salicylic acid or its derivative of 6.5 to less than 7.0in pH to an aqueous solution of chromium(III) halide of 3.0 to 5.8 inpH.

[0013] Further, according to the present invention, there is provided acharge control agent to be used in a toner for developing anelectrostatic latent image, which comprises a trivalent chromium salt ofsalicylic acid or its derivative prepared by adding an aqueous solutionof an alkali metal salt of salicylic acid or its derivative of 6.5 toless than 7.0 in pH to an aqueous solution of chromium(III) halide of3.0 to 5.8 in pH.

[0014] Further, according to the present invention, there is provided atoner for developing an electrostatic latent image, which contains atrivalent chromium salt of salicylic acid or its derivative prepared byadding an aqueous solution of an alkali metal salt of salicylic acid orits derivative of 6.5 to less than 7.0 in pH to an aqueous solution ofchromium(III) halide of 3.0 to 5.8 in pH.

BRIEF DESCRIPTION OF THE DRAWING

[0015]FIG. 1 is a graph showing an X-ray diffraction pattern at anordinary temperature of the starting material,3,5-di-tert-butylsalicylic acid and that of trivalent chromium salt of3,5-di-tert-butylsalicylic acid prepared according to the presentinvention.

[0016]FIG. 2 is a graph showing X-ray diffraction patterns at severalelevated temperatures of trivalent chromium salt of3,5-di-tert-butylsalicylic acid prepared according to the presentinvention.

[0017]FIG. 3 is a graph showing an ESR (Electron Spin Resonance)spectrum of trivalent chromium salt of 3,5-di-tert-butylsalicylic acidprepared according to the present invention.

[0018]FIG. 4 is a graph showing an infrared absorption spectrum of thestarting material, 3,5-di-tert-butylsalicylic acid and that of trivalentchromium salt of 3,5-di-tert-butylsalicylic acid produced according tothe present invention.

[0019]FIG. 5 is a graph showing ¹³C-NMR spectrum of trivalent chromiumsalt of 3,5-di-tert-butylsalicylic acid prepared according to thepresent invention.

[0020]FIG. 6 is a graph showing FD-MS spectrum of trivalent chromiumsalt of 3,5-di-tert-butylsalicylic acid prepared according to thepresent invention.

DETAILED DESCRIPTION AND PREFERRED EMBODIMENT OF THE INVENTION

[0021] As has been described herein before, trivalent chromium salts ofsalicylic acid or its derivative of the present invention useful ascharge control agents are prepared by adding an aqueous solution of analkali metal salt of salicylic acid or its derivative of 6.5 to lessthan 7.0 in pH to an aqueous solution of a chromium(III) halide of 3.0to 5.8 in pH.

[0022] A preferred salicylic acid or its derivative used in theabove-described process is a compound represented by the followinggeneral formula 1;

[0023] wherein

[0024] R¹, R² and R³ each represents a hydrogen atom, a saturated orunsaturated, straight or branched alkyl group or, when taken together,R¹ and R² or R² and R³ form a fused ring optionally having a saturatedor unsaturated, straight or branched alkyl group.

[0025] The trivalent chromium salt of salicylic acid or its derivativeprepared according to the above-described process of the presentinvention by using salicylic acid or its derivative represented bygeneral formula 1 is represented by the following general formula 2;

[0026] wherein

[0027] R¹, R² and R³ each represents a hydrogen atom, a saturated orunsaturated, straight or branched alkyl group or, when taken together,R¹ and R² or R² and R³ form a fused ring optionally having a saturatedor unsaturated, straight or branched alkyl group, and n represents 0, 1or 2.

[0028] As to pH value of the aqueous solution of chromium(III) halide tobe used in the above-described process of the present invention, apreferred range varies depending upon whether R¹ and R² or R² and R³ ofsalicylic acid or its derivative form a fused ring or not. That is,where R¹ and R² or R² and R³ of salicylic acid or its derivative do notform a fused ring, pH of the aqueous solution of chromium(III) halide ispreferably 3.8 to 4.1, more preferably 3.9 to 4.02 and, where R¹ and R²or R² and R³ of salicylic acid or its derivative form a fused ring, pHof the aqueous solution of chromium(III) halide is preferably 4.5 to5.8, more preferably 5.0 to 5.5. If pH of the aqueous solution ofchromium(III) halide is outside the scope of 3.0 to 5.8, it becomesdifficult to form intended trivalent chromium salt of salicylic acid orits derivative or, if formed, with a decreased yield, thus beingpractically problematical.

[0029] The above-described aqueous solution of chromium(III) halide of3.0 to 5.8 in pH is prepared by gradually adding an aqueous solution ofalkali metal hydroxide to an aqueous solution of chromium(III) halide(pH 1.9- 2.3) spending enough time. As the aqueous solution of alkalimetal hydroxide, an aqueous solution of NaOH of usually about 0.5 toabout 2% (by weight, and “%” represent ‘% by weight’ hereinafter) inconcentration, for example, about 1% is used and, as the aqueoussolution of chromium(III) halide, an aqueous solution of chromium(III)halide of usually about 5 to about 20%, for example, about 10% is used.If concentration of the aqueous solution of the alkali metal hydroxideis less than 0.5%, it will take a prolonged period of time to adjust pH,while if more than 2%, chromium hydroxide is liable to be formed. Thethus prepared aqueous solution of chromium(III) halide (pH 3.0 to 5.8)is desirably introduced directly without allowing to stand to the nextstep, because the aqueous solution would suffer reduction in pH uponbeing allowed to stand.

[0030] On the other hand, the aqueous solution of alkali metal salt ofsalicylic acid or its derivative to be used for the reaction has a pH of6.5 to less than 7.0, preferably 6.7 to 6.9. This aqueous solution ofalkali metal salt of salicylic acid or its derivative is usuallyprepared by adding salicylic acid or its derivative in an about equalmolar amount based on alkali metal to an alkali metal aqueous solutionof about 0.5 to about 5% , for example, 1 to 2% in concentration heatedto usually 50 to 70° C., preferably about 60° C. to about 65° C., andstirring this aqueous solution with keeping its temperature at thislevel to thereby dissolve salicylic acid or its derivative. If pH of theaqueous solution of the alkali metal salt of salicylic acid or itsderivative is less than 6.5, there results much insoluble matters in theformed solution whereas, if 7.0 or more in pH, there is formed Cr(OH)₃,thus not being favorable. If the pH of said aqueous solution is withinthe range of from 6.7 to 6.9, the salicylic acid or its derivativerepresented by the foregoing general formula 2 can be obtained in a highyield, thus pH of the aqueous solution being preferably 6.7 to 6.9.Temperature for preparing the aqueous solution of the alkali metal saltof salicylic acid or its derivative is to be decided taking solubilityof the alkali metal salt of salicylic acid or its derivative intoconsideration, and hence the temperature of the above-described range isusually employed.

[0031] Further, upon adding the aqueous solution of alkali metal salt ofsalicylic acid or its derivative having a pH of 6.5 to less than 7.0 tothe aqueous solution of chromium(III) halide of 3.0 to 5.8 in pH, it ispreferred to gradually add with spending enough period of time, sincerapid addition of the aqueous solution of alkali metal salt woulddecrease the yield. Chromium(III) halide is usually used in an amount of1 mol or more based on 3 mols of salicylic acid or its derivative,preferably more than 1 mol. After completion of the dropwise addition ofthe aqueous solution of the alkali metal salt of salicylic acid or itsderivative, stirring is continued for an enough period of time, forexample, about one hour, to complete the reaction. Then, the reactionmixture is filtered to collect the reaction product, followed bywashing, drying and pulverizing the product to obtain the end productcontaining the compound represented by the general formula 2 useful as acharge control agent. In this occasion, temperature of the aqueoussolution of chromium(III) halide of 3.0 to 5.8 in pH, temperature of theaqueous solution of alkali metal salt of salicylic acid or itsderivative, temperature of the mixture of these solutions, andtemperature upon suction filtration are usually kept in the range offrom about 50 to about 70°C., preferably 60 to 65° C. Filtration can beconducted in a conventionally known manner such as suction filtration,centrifugation or the like. As the salicylic acid derivatives to be usedin the present invention, those represented by the foregoing generalformula 1 are preferred. Preferred examples of the substituents R¹, R²and R³ in the general formula 1 include a straight or branched alkylgroup containing 1 to 12 carbon atoms such as a methyl group, an ethylgroup, a propyl group, an isopropyl group, a butyl group, an isobutylgroup, a sec-butyl group, a tert-butyl group, an amyl group, an isoamylgroup, an octyl group, a tert-octyl group, a dodecyl group, etc. and anunsaturated alkyl group such as an allyl group, a propenyl group, abutenyl group, etc. Of these, saturated or unsaturated, straight orbranched alkyl groups containing 1 to 8 carbon atoms are more preferred,with a tert-butyl group and a tert-octyl group being particularlypreferred. When R¹ and R² or R² and R³ are taken together to form afused ring optionally having a saturated or unsaturated, straight orbranched alkyl group, they preferably form a benzene ring, thus thesalicylic acid or its derivative being a hydroxynaphthoic acid typecompound. Particularly preferred specific examples of the salicylic acidor its derivative include 3,5-di-tert-butylsalicylic acid and3-hydroxy-2-naphthoic acid.

[0032] The toner of the present invention for developing anelectrostatic latent image contains, as a charge control agent,trivalent chromium salt of salicylic acid or its derivative preparedaccording to the above-described process of the present invention. Thecharge control agent contains at least trivalent chromium salt ofsalicylic acid or its derivative represented by the foregoing generalformula 2. As to the charge control agent, it suffices to use it in anamount necessary to impart desired charge to the toner. For example, thecharge control agent is preferably added in an amount of about 0.05 toabout 10 parts by weight per 100 parts by weight of resin.

[0033] As constituents of the toner of the present invention fordeveloping an electrostatic latent image, known materials forconstituting toner such as binder resins, colorants or powder ofmagnetic material, and if necessary, releasing agents, lubricants,flowability-improving agents, abrasives, conductivity-imparting agents,image delamination-preventing agents, etc. may be used in addition tothe charge control agent of the present invention. Additionally, theremay be used other known negatively chargeable charge control agents suchas azo dyes containing a metal (e.g., Cr, Co, Al or Fe), charge controlagent which is resin type(CCR), etc. in addition to the charge controlagent of the present invention. The amount of such other charge controlagents are not particularly limited as long as the effect of the chargecontrol agent of the present invention is attained.

[0034] As a binder resin to be used for the toner of the presentinvention for developing an electrostatic latent image, any of known onemay be used that is conventionally known as a binder resin for tonersfor developing an electrostatic latent image. The usable binder resin isexemplified by homopolymers of styrene or its derivative such aspolystyrene, poly-p-chlorostyrene, polyvinyltoluene, etc.; styrenecopolymers such as a styrene-p-chlorostyrene copolymer, astyrene-vinyltoluene copolymer, a styrene-vinylnaphthalene copolymer, astyrene-acrylate copolymer, a styrene-methacrylate copolymer, astyrene-methyl α-chloromethacrylate copolymer, a styrene-acrylonitrilecopolymer, a styrene-vinyl methyl ether copolymer, a styrene-vinyl ethylether copolymer, a styrene-vinyl methyl ketone copolymer, a styrene-butadiene copolymer, a styrene-isoprene copolymer, astyrene-acrylonitrile-indene copolymer, etc.; polyvinyl chloride; phenolresin; natural resin-modified phenol resin; natural resin-modifiedmaleic acid resin; acrylic resin; methacrylic resin; polyvinyl acetate;silicone resin; polyester resin; polyurethane; polyamide resin; furanresin; epoxy resin; xylene resin; polyvinyl butyral; terpene resin;cumarone-indene resin; petroleum resin; etc.

[0035] In addition, cross-linked styrene copolymers are also preferredbinder resins. As the comonomer for styrene monomer of the styrenecopolymers, there may be used one or more of monocarboxylic acids havinga double bond or derivatives thereof such as acrylic acid, methylacrylate, ethyl acrylate, butyl acrylate, dodecyl acrylate, octylacrylate, 2-ethylhexyl acrylate, phenyl acrylate, methacrylic acid,methyl methacrylate, ethyl methacrylate, butyl methacrylate, octylmethacrylate, acrylonitrile, methacrylonitrile, acrylamide, etc.;dicarboxylic acids having a double bond or derivatives thereof such asmaleic acid, methyl maleate, butyl maleate, dimethyl maleate, etc.;vinyl esters such as vinyl chloride, vinyl acetate, vinyl benzoate,etc.; ethylenic olefins such as ethylene, propylene, butylene, etc.;vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone, etc.;vinyl ethers such as vinyl methyl ether, vinyl ethyl ether, vinylisobutyl ether, etc.; and the like.

[0036] As the cross linking agents; those compounds which have two ormore polymerizable double bonds are mainly used. For example, aromaticdivinyl compounds such as divinylbenzene, divinylnaphthalene, etc.;carboxylic esters having two double bonds such as ethylene glycoldiacrylate, ethylene glycol dimethacrylate, 1,3-butanedioldimethacrylate, etc.; divinyl compounds such as divinylaniline, divinylether, divinyl sulfide, divinyl sulfone, etc.; and compounds havingthree or more vinyl groups may be used alone or in combination.Particularly, styrene copolymers having a molecular weight distributionmeasured according to GPC wherein at least one peak exists in the regionof from 3×10³ to 5×10⁴ and at least one peak or a shoulder exists in theregion of from 10⁵ above are preferred in view of fixing properties.

[0037] Molecular weight distribution is measured according to GPC underthe following conditions: A column is stabilized in a 40° C. heatchamber, and about 100 μl of a test sample solution in tetrahydrofuran(THF) is injected into the column at the temperature while introducingthere into THF as a solvent at a flow rate of 1 ml/min to measure. Uponmeasurement of the molecular weight of the sample, molecular weightdistribution of the sample was calculated based on the relation betweenthe logarithmic value of calibration curve prepared from severalmonodisperse polystyrene standard samples and the count number. As thestandard polystyrene samples for preparing the calibration curve, thosewhich have a molecular weight of about 10² to about 10⁷ manufactured by,for example, TOSO K.K. or SHOWA DENKO K.K. are used, with at least about10 points being preferably plotted. As a detector, an RI (RefractionIndex) detector is used. Additionally, as the column, a plurality ofcommercially available polystyrene gel column are preferably used. Forexample, a combination of Shodex GPC KF-801, 802, 803, 804, 805, 806,807 and 800P manufactured by SHOWA DENKO K.K. or a combination of TSKgel G100OH(H_(XL)), G2000H(H_(XL)), G3000H(H_(XL)), G4000H(H_(XL)),G5000H(H_(XL)), G6000H(H_(XL)), G7000H(H_(XL)), TSK guard columnmanufactured by TOSO K.K. may be used.

[0038] Test samples are prepared in the following manner. A sample isplaced in THF and, after allowing to stand for several hours, themixture is sufficiently shook till no insoluble matters of the sampleexist, followed by allowing the mixture to stand for 12 hours or longer.In this occasion, the sample is to be allowed to stand in THF for 24hours or longer in total. Then, the mixture is passed through asample-processing filter (pore size: 0.45 to 0.5 μm; e.g., MAI SHORIDISC H-25-5 made by TOSO K.K. or EKIKURO DISC 25CR made by GermanScience Japan K.K.) to prepare a sample for GPC. Sample concentration isadjusted so that the resin component is contained in a concentration of0.5 to 5 mg/ml.

[0039] Additionally, a polymerization initiator is used upon productionof the vinyl polymer. As the polymerization initiator, any ofconventionally known ones may be used. For example, benzoyl peroxide,lauroyl peroxide, tert-butyl hydroperoxide, tert-butyl peroxybenzoate,di-tert-butyl peroxide, cumene hydroperoxide, dicumyl peroxide,azoiso-butylonitrile, azobisvaleronitrile, etc. may favorably be used.These initiators are used generally in an amount of 0.2 to 5% by weightbased on vinyl monomer. Polymerization temperature is properly selecteddepending upon kinds of a monomer and an initiator to be used.

[0040] Polyester resins are also preferred as binder resins for thetoner of the present invention for developing an electrostatic latentimage. As the alcohol component constituting such polyester resins,there are illustrated diols such as ethylene glycol, propylene glycol,1,3-butanediol, 1,4-butanediol, 2,3-butanediol, diethylene glycol,triethylene glycol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol,2-ethyl-1,3-hexanediol, hydrogenated bisphenol A, bisphenol derivativesrepresented by the following general formula 3 etc.; and polyhydricalcohols such as glycerin, sorbitol, sorbitan, etc.

[0041] wherein

[0042] R represents an ethylene or propylene group, x and y eachrepresents an integer of 1 or more, provided that the average of x+y is2 to 10.

[0043] As the acid component, there are illustrated dicarboxylic acidssuch as benzenedicarboxylic acids or the anhydrides thereof (e.g.,phthalic acid, terephthalic acid, isophthalic acid, phthalic anhydride,etc.), alkyldicarboxylic acids or the anhydrides thereof (e.g., succinicacid, adipic acid, sebacic acid, azelaic acid, etc.), succinic acidsubstituted by an alkyl group containing 16 to 18 carbon atoms or theanhydrides thereof, unsaturated dicarboxylic acids or the anhydridesthereof (e.g., fumaric acid, maleic acid, citraconic acid, itaconicacid, etc.); and carboxylic acids having 3 or more carboxyl groups(e.g., trimellitic acid, pyromellitic acid, benzophenonetetracarboxylicacid, and the anhydrides thereof, etc.).

[0044] Preferred alcohol components are those bisphenol derivativeswhich are represented by the foregoing general formula 3, and preferredacid components are dicarboxylic acids such as phthalic acid,terephthalic acid, isophtalic acid, or its anhydride, succinic acid,n-dodecenylsuccinic acid or its anhydride, fumaric acid, maleic acid,maleic anhydride, etc.; and tricarboxylic acids such as trimellitic acidor its anhydride.

[0045] The above-described polyester resins preferably have an acidvalue of 40 mg KOH/g or less as a toner. If the acid value is 40 mgKOH/g or less, serious deterioration of abrasion charging property canbe prevented even when left in a high-humidity environment for a longperiod of time, thus such acid value being preferred. More preferably,the acid value be 30 mg KOH/g or less, since abrasion charging propertyis stabilized even when the number of copies increases. In particular,polyester resins having the toner acid value of from 1 to 20 mg KOH/gare preferred, since no deterioration of frictional electrificationproperty takes place even after being left in a high-humidityenvironment for a long period of time, and the toner acquires completelythe same electrified quantity as before being left upon being shook witha carrier, with the charging rate being rapid and no gradual increase inelectrified quantity taking place as the number of copies increases.

[0046] Additionally, in the present invention, measurement of acid valuemay be conducted by applying the method of JIS K-0070. The acid value isrepresented in terms of the amount of potassium hydroxide in mgnecessary for neutralizing 1 g of the toner. With toners containing amagnetic material, however, the magnetic material is previouslydissolved away with an acid, and 1 g of the residue is used as thesample to be neutralized.

[0047] In the case of employing a pressure-fixing process, binder resinsfor pressure-fixable toners may be used. For example, there areillustrated polyethylene, polypropylene, polymethylene, polyurethaneelastomer, ethylene-ethyl acrylate copolymers, ethylene-vinyl acetatecopolymers, ionomer resins, styrene-butadiene copolymers,styrene-isoprene copolymers, linear saturated polyesters, paraffins,etc.

[0048] As colorants for the toner of the present invention fordeveloping an electrostatic latent image, any of those which haveconventionally been used in production of toners may be used. Examplesof such colorants include metal salts of fatty acids, various types ofcarbon black, and dyes and pigments of phthalocyanine, Rhodamine,quinacridone, triarylmethane, anthraquinone, azo, diazo, etc. These maybe used alone or as a mixture of two or more of them.

[0049] The toner of the present invention for developing anelectrostatic latent image may contain a powder of magnetic material.Usable magnetic materials may be any of those alloys, compounds, etc.which contain a ferromagnetic element and have conventionally been usedin producing magnetic toners. Examples of such magnetic materialsinclude iron oxides or compounds of a divalent metal and iron oxide suchas magnetite, maghetite, ferrite, etc., metals such as iron, cobalt,nickel, etc., alloys thereof with a metal such as aluminum, cobalt,copper, lead, magnesium, tin, zinc, antimony, beryllium, bismuth,cadmium, calcium, manganese, selenium, titanium, tungsten, vanadium,etc., and a mixture thereof. These magnetic materials have an averageparticle size of preferably about 0.1 to about 2 μm, and more preferablyabout 0.1 to about 0.5 μm. The magnetic material may be contained in thetoner in an amount of from about 20 to about 200 parts by weight,preferably 40 to 150 parts by weight, based on 100 parts by weight ofthe thermoplastic resin. The toner preferably has a saturationmagnetization of 15 to 35 emu/g (measured in a magnetic field of 10kOe).

[0050] The toner of the present invention may be mixed with a carrier touse as a two-component toner. As the carrier to be used together withthe toner of the present invention, any of conventionally known carriersmay be used. As carriers to be used, there are illustrated, for example,a magnetic powder such as an iron powder, a ferrite powder, a nickelpowder, etc., glass beads, and a magnetic powder or beadssurface-treated with a resin or the like. Resins for treating (coating)the surface of carrier particles include a styrene-acrylic estercopolymer, a styrene-methacrylic ester copolymer, an acrylic estercopolymer, a methacrylic ester copolymer, a fluorine-containing resin, asilicon-containing resin, a polyamide resin, an ionomer resin, apolyphenylene sulfide resin, etc. or a mixture thereof. Of these,fluorine-containing resins and silicon-containing resins areparticularly preferred since they form a less amount of spent toner.

[0051] The toner of the present invention containing the charge controlagent preferably has a weight average particle size of 3 to 15 μm. Morepreferably, the toner has a particle size distribution wherein tonerparticles having a particle size of 5 μm or less account for 12 to 60%by number of particles, toner particles having a particle size of 8 to12.7μm account for 1 to 33% by number of particles, and toner particleshaving a particle size of 16 μm or more account for 2.0% by weight ofparticles or less and has a weight average particle size of 4 to 10 μmin view of developing properties. Additionally, particle sizedistribution of the toner can be measured by, for example,Coalter-Counter method.

[0052] The toner of the present invention may further contain, ifnecessary, known additives having been used in production of toners suchas a releasing agent, a lubricant, a flowability-improving agent, anabrasive, a conductivity-imparting agent, a imagedelamination-preventing agent, etc. which may be used internally orexternally. Examples of the releasing agent include, for example,wax-like substances such as low molecular weight polyethylene, lowmolecular weight polypropylene, microcrystalline wax, carnauba wax,sazol wax, paraffin wax, etc. These may be added to the toner in anamount of usually from about 0.5 to about 5% by weight. Examples of thelubricant include polyvinylidene fluoride, zinc stearate, etc., examplesof the flowability-improving agent include colloidal silica, aluminumoxide, titanium oxide, etc., examples of the abrasive include ceriumoxide, silicon carbide, strontium titanate, tungsten carbide, calciumcarbonate, etc., and examples of the conductivity-imparting agentinclude carbon black, tin oxide, etc. Fine powders offluorine-containing polymers such as polyvinylidene fluoride etc. arepreferred in view of flowability, abrasive property, charge stability,etc.

[0053] The toner of the present invention can be produced according to aconventionally known process for producing toners. Generally, theabove-described -toner constituents are well mixed in a mixer such as aball mill, a Henschel mixer, etc., well kneaded using a hot rollkneader, a uniaxial or biaxial extruder or like hot kneader and, aftercooling to solidify, mechanically roughly crushed using a crushingmachine such as a hammer mill etc., then finely pulverized by a jet millor the like, followed by classification. However, the process forproducing the toner is not limited only to the above-described process,but there may be arbitrarily employed other processes such as a processof dispersing other constituents than a binder resin in the solution ofbinder resin, and spray-drying the dispersion, a so-calledmicroencapsulation process, a polymerization process of conductingemulsion or suspension polymerization of monomers for preparing thebinder resin under the existence of other constituent for toner, etc.

[0054] The process of the present invention for preparing the chargecontrol agent, the toner of the present invention for developing anelectrostatic latent image, and process for producing the toner are nowdescribed in more detail by reference to the following Examples which,however, are construed to be illustrative and not construed to belimitative at all.

EXAMPLE 1

[0055] Preparation of Chromium(III) 3,5-di-tert-butylsalicylate

[0056] 450 g of water and 7.2 g of NaOH were placed in a 500-cc beaker,and the mixture was heated under stirring to completely dissolve NaOH.This NaOH aqueous solution was heated to 65° C., and 45 g of3,5-di-tert-butylsalicylic acid was added thereto under stirring. Themixture was further stirred while keeping the temperature at 65° C. todissolve 3,5-di-tert-butylsalicylic acid. When pH of the dissolvedsolution became 6.8, heating and stirring were discontinued, and thesolution was filtered to remove insoluble 3,5-di-tert-butylsalicylicacid, thus a brown filtrate being obtained. Separately, 37.2 g of a 40%CrCl₃ solution and 120 g of water were placed in a 500-cc beaker toprepare a chromium(III) chloride solution having a pH of 2.1. To thischromium(III) chloride solution was gradually added 120 g of 1% NaOHaqueous solution with spending enough time to obtain a solution of 3.95in pH. Then, this solution was transferred into a 2-liter beaker, anddiluted with water to make the total amount 350 g. This chromium(III)chloride solution was heated to 60° C. and, under stirring, theabove-described solution of 3,5-di-tert-butylsalicylic acid kept at 60°C. was dropwise added thereto over a period of time of 1.5 to 2 hours.As the addition proceeded, the reaction solution gradually assumed alight green color. After completion of the dropwise addition, stirringwas further continued for 1 hour at a temperature of 60 to 65° C., andthe reaction solution was suction filtered and washed with water toobtain 170 g of a reaction product (wet). The pH of the filtrate was4.00. The reaction product collected by filtration was dried at 50° C.for about 14 hours, and the dried product was pulverized to obtain 70 gof an end product. The reaction product is completely soluble in carbontetrachloride.

[0057] The reaction product was subjected to X-ray diffractionmeasurement, ESR (Electron Spin Resonance) measurement, IR (Infrared)spectrum measurement, ¹³C-NMR (Nuclear Magnetic Resonance) measurementand FD-MS (Mass Spectrum) measurement to obtain the results shown inFIGS. 1 to 6. FIG. 1 shows the X-ray diffraction pattern of the startingmaterial 3,5-di-tert-butylsalicylic acid and that of the reactionproduct measured at an ordinary temperature. In FIG. 1, solid linecorresponds to the reaction product and broken line to3,5-di-tert-butylsalicylic acid. The results of the measurement revealthat the reaction product does not have a peak derived from the startingmaterial, and does not have such a high crystallinity.

[0058]FIG. 2 shows an X-ray diffraction pattern of the reaction productmeasured at an elevated temperature. A peak at 2θ=31.64 becomes clear byheating. This result reveals that the reaction product contains crystalwater.

[0059]FIG. 3 shows results of measurement of ESR of the reactionproduct. A signal for chromium is detected at g=1.98, and the valencenumber of Cr metal is three since width of the signal is broad. Divalentchromium does not give any signal, whereas 5-valent chromium gives asharp signal at g=1.98.

[0060]FIG. 4 shows infrared absorption spectra of the starting material,3,5-di-tert-butylsalicylic acid and the reaction product. In FIG. 4,solid line shows an infrared absorption spectrum for the reactionproduct and broken line for 3,5-di-tert-butylsalicylic acid. Thereaction product shows a big absorption at 1550 cm⁻¹ which is a peak for—COO— (carboxylate), whereas the starting material,3,5-di-tert-butylsalicylic acid shows no absorption at 1550 cm⁻¹. Fromthese results, it seems that —H of the carboxyl group of3,5-di-tert-butylsalicylic acid is removed and forms a metal salt (Crsalt).

[0061]FIG. 5 shows the results of measurement of ¹³C-NMR of the reactionproduct. In FIG. 5, main peaks are assigned. From the results, thereaction product is speculated to be a Cr salt of3,5-di-tert-butylsalicylic acid.

[0062]FIG. 6 shows an FD-MS (mass spectrum) of the reaction product. Asis clear from FIG. 6, the reaction product is considered to be amixture. Main compound in the reaction product is a substance having amolecular weight of 885. This is surmised to be a trivalent Cr salt of3,5-di-tert-butylsalicylic acid monohydrate (molecular weight:863).

[0063] Besides, mass spectrometry by ICP-MS gave the result of 76,800with Cr. This result reveals that the content of Cr (trivalent) of thethus obtained compound is 7.68% by weight but, since theoretical amount(wt %) of Cr in the Cr (trivalent) salt of 3,5-di-tert-butylsalicylicacid monohydrate is 6.03, it seems that the product contains otherproducts than Cr(trivalent) salt of 3,5-di-tert-butylsalicylic acid.

[0064] From these analytical results, the reaction product is consideredto be a mixture containing as a major component a salt of trivalent Crwith 3 mols of 3,5-di-tert-butylsalicylic acid to which salt onemolecule of water is added. A reason for the presence of manyco-existing compounds may be that hexa-aqua ion is instantly producedupon dissolution of chromium chloride in water, leading to the followingequilibrium state. However, this is merely a speculation of the inventorand does not limit the present invention at all.

EXAMPLE 2

[0065] Styrene-n-butyl methacrylate copolymer 93 parts by weightPhthalocyanine Blue 5 parts by weight Compound obtained in Example 1 2parts by weight

[0066] The above components were mixed in a Henschel mixer, then kneadedin a biaxial heating kneader, and the mixture extruded from the kneaderwas cooled at a room temperature, roughly crushed in a hammer mill,finely pulverized in a jet mill pulverizer. The pulverized powder wasclassified in a classifying machine to collect a portion having anaverage particle size of 9 μm. Thus, a blue toner was obtained. 100parts by weight of this toner powder was mixed with 0.5 part by weightof hydrophobic silica (Aerosil R974) functioning as a fluidizing agentand 1 part by weight of rutile type titanium oxide having been treatedwith stearic acid and functioning as an abrasive. This toner mixture wasmixed with a carrier (silicone resin-coated spherical ferrite having aparticle size of about 70 μm) to obtain a two-component developercontaining the toner in an amount of 5% by weight. The electrifiedamount of this developer measured by Blow-off Method was 30 μc/g.

[0067] Copies were made using the above prepared developer by acommercially available electrophotographic copier under theenvironmental conditions of 10° C. and 20 RH, 23° C. and 50 RH, and 30°C. and 85 RH. Under any of these conditions, there were obtained clear,blue copies with no fog and no offset. Even after continuously making50,000 copies under the environmental conditions of 10° C. and 20 RH,and 23° C. and 50 RH, the quality of the copies was not lowered.Furthermore, 10,000 copies were continuously made under theenvironmental conditions of 30° C. and 85 RH, but the quality of thecopies was not deteriorated.

COMPARATIVE EXAMPLE 1

[0068] A comparative two-component developer was prepared in quite thesame manner as in Example 1 except that azo chromium compound (TRH,manufactured by Hodogaya Kagaku K.K.) was used as a charge control agentin place of the compound obtained in Example 1. The electrified amountof this developer measured by Blow-off Method was 30 μc/g. A copy wasmade using the above prepared comparative developer in the same manneras in Example 1, thus producing a copy of blue tone. After continuouslymaking 5,000 copies, there were obtained blurred copies with foa.

EXAMPLE 3

[0069] Polyester (Runapel 1448, manufactured 59.8 parts by by ArakawaKagaku K.K.) weight Magnetic substance (magnetite) 38.0 parts by weightWax (polypropylene) 1.5 parts by weight Compound obtained in Example 10.7 part by weight

[0070] The above components were mixed in a Henschel mixer, then kneadedin a biaxial heating kneader, and the mixture extruded from the kneaderwas cooled at a room temperature, roughly crushed in a hammer mill,finely pulverized in a jet mill pulverizer. The pulverized powder wasclassified in a classifying machine to collect a portion having anaverage particle size of 9 μm. Thus, a magnetic toner was obtained. Theelectrified amount of this toner measured by Blow-off Method was 15μc/g. 100 parts by weight of this toner powder was mixed with 0.3 partby weight of hydrophobic silica (Aerosil R972), 0.2 part by weight ofsilicone resin-coated anatase type titanium oxide and 1 part by weightof calcium carbonate having been treated with a silane coupling agent toobtain a magnetic one-component developer.

[0071] Copies were made using the above prepared developer by acommercially available electrophotographic copier under theenvironmental conditions of 10° C. and 20 RH, 23° C. and 50 RH, and 30°C. and 85 RH. Under any of these conditions, there were obtained clear,black toner images with no fog and no offset. Even after continuouslymaking 150,000 copies under the environmental conditions of 10° C. and20 RH, 150,000 copies under 30° C. and 85 RH, and 200,000 copies under23° C. and 50 RH, the quality of the copies (500,000 copies in all) wasnot lowered to the last copy.

COMPARATIVE EXAMPLE 2

[0072] A comparative magnetic one-component developer was prepared inquite the same manner as in Example 3 except that azo chromium compound(S-34, manufactured by Orient K.K.) was used as a charge control agentin place of the compound obtained in Example 1.

[0073] Copying was continuously conducted using the above preparedcomparative developer in a commercially available electrophotographiccopier under the environmental conditions of 30° C. and 85 RH but, when5,000 copies were made, image density was so lowered that the test wasdiscontinued.

EXAMPLE 4

[0074] 25 g of NaOH was added to 900 g of water, and the mixture washeated under stirring to completely dissolve NaOH. To this NaOH aqueoussolution was added 112.8 g of 3-hydroxy-2-naphthoic acid under stirringto dissolve 3-hydroxy-2-naphthoic acid. When pH of the dissolvedsolution became 6.9, heating and stirring were discontinued, and thesolution was filtered to remove insolubles to prepare a reactionsolution A. Separately, 119 g of a 40% CrCl₃ solution was added to 500 gof water and stirred to prepare a chromium(III) chloride solution. Tothis solution was gradually dropwise added 380 g of a 1% NaOH aqueoussolution in 2.5 hours to obtain a solution having a pH of 5 to 5.5. Thissolution was referred to as reaction solution B. Then, reaction solutionB was dropwise added to reaction solution A slowly in about 2 hours.After completion of the dropwise addition, the reaction solution washeated to 70 to 75° C., then cooled to 50° C. and the reaction solutionwas suction filtered and washed with water to obtain a reaction product.The pH of the filtrate was 4.5. The reaction product collected byfiltration was dried at 80° C. to obtain 150 g of an end product.

EXAMPLE 5

[0075] A magnetic one-component developer was prepared in quite the samemanner as in Example 3 except that the compound obtained in Example 4was used as a charge control agent in place of the compound obtained inExample 1.

[0076] Copies were made using the above prepared developer by acommercially available electrophotographic copier under theenvironmental conditions of 10° C. and 20 RH, 23° C. and 50 RH, and 30°C. and 85 RH. Under any of these conditions, there were obtaineddistinct, black toner images with no fog and no offset. Even aftercontinuously making 150,000 copies under the environmental conditions of10° C. and 20 RH, 150,000 copies under 30° C. and 85 RH, and 50,000copies under 23° C. and 50 RH, the quality of the copies (350,000 copiesin all) was not lowered.

EXAMPLE 6

[0077] Polyester (Runapel 1448, manufactured 48.9 parts by by ArakawaKagaku K.K.) weight Magnetic substance (magnetite) 45.0 parts by weightWax (polypropylene) 1.6 parts by weight Compound obtained in Example 10.5 part by weight CCR (FCA-101, manufactured by Fujikura 4.0 parts byKasei K.K.) weight

[0078] The above components were mixed in a Henschel mixer, then kneadedin a biaxial heating kneader, and the mixture extruded from the kneaderwas cooled at a room temperature, roughly crushed in a hammer mill,finely pulverized in a jet mill pulverizer. The pulverized powder wasclassified in a classifying machine to collect a portion having anaverage particle size of 9 μm. Thus, a magnetic toner was obtained. Theelectrified amount of this toner measured by Blow-off Method was 15μc/g. 100 parts by weight of this toner powder was mixed with 0.4 partby weight of hydrophobic silica (Aerosil R972), 0.1 part by weight ofanatase type titanium oxide having been treated with a silane couplingagent and 1 part by weight of calcium carbonate having been treated withan aminosilane coupling agent to obtain a magnetic one-componentdeveloper.

[0079] Copies were made using the above prepared developer by acommercially available electrophotographic copier under theenvironmental conditions of 10° C. and 20 RH, 23° C. and 50 RH, and 30°C. and 85 RH. Under any of these conditions, there were obtaineddistinct, black toner images with no fog and no offset. Even aftercontinuously making 150,000 copies under the environmental conditions of10° C. and 20 RH, 150,000 copies under 30° C. and 85 RH, and 50,000copies under 23° C. and 50 RH, the quality of the copies (350,000 copiesin all) was not lowered.

[0080] As can be seen from the above Examples, the novel trivalentchromium salt of salicylic acid or salicylic acid derivative, which isobtained by the process of the present invention by reactingchromium(III) halide with an alkali metal salt of salicylic acid or itsderivative represented by the general formula 1 under specificconditions, can provide a toner having good storage stability, causingno change in copied image density and no fog even when repeatedly used,and providing good toner images under various environment conditions.The toner has no troubles about fixing properties and offset problemand, as a color toner, can provide distinct color images.

[0081] It will be appreciated by those skilled in the art thatvariations in the invention disclosed herein may be made withoutdeparting from the spirit of the invention. The invention is not to belimited by the specific embodiments disclosed herein, but only by thescope of the claims appended hereto.

What is claimed is:
 1. A process for producing a trivalent chromium saltof salicylic acid or its derivative, which comprises adding an aqueoussolution of an alkali metal salt of salicylic acid or its derivative of6.5 to less than 7.0 in pH to an aqueous solution of chromium(III)halide of 3.0 to 5.8 in pH.
 2. The process for producing a trivalentchromium salt of salicylic acid or its derivative as described in claim1 , wherein said salicylic acid or its derivative is a compoundrepresented by the following general formula 1;

wherein R¹, R² and R³ each represents a hydrogen atom, a saturated orunsaturated, straight or branched alkyl group or, when taken together,R¹ and R²or R² and R³ form a fused ring optionally having a saturated orunsaturated, straight or branched alkyl group.
 3. The process forproducing a trivalent chromium salt of salicylic acid or its derivativesdescribed in claim 2 , wherein said salicylic acid derivativerepresented by the foregoing general formula 1 is3,5-di-tert-butylsalicylic acid or 3-hydroxy-2-naphthoic acid.
 4. Acharge control agent to be used in a toner for developing anelectrostatic latent image, which comprises a trivalent chromium salt ofsalicylic acid or its derivative prepared by one of the processesdescribed in claims 1 to 3 .
 5. A toner for developing an electrostaticlatent image, which contains the charge control agent described in claim4 .
 6. A toner for developing an electrostatic latent image, whichcontains a trivalent chromium salt of salicylic acid or its derivativerepresented by the following general formula 2;

wherein R¹, R² and R³ each represents a hydrogen atom, a saturated orunsaturated, straight or branched alkyl group or, when taken together,R¹ and R² or R² and R³ form a fused ring optionally having a saturatedor unsaturated, straight or branched alkyl group, and n represents 0, 1or 2.